Ultrafast Detonation of Hydrazoic Acid: Insights from Many-body Molecular Dynamics Force Fields*

In this work, we present the development and application of the Chebyshev Interaction Model for Efficient Simulations (ChIMES) to the study of hydrazoic acid (HN₃) under detonation. Computational study of HN₃ is challenging due to its ultrafast detonation, i.e. the chemical decomposition to stable products is complete in less than 10 ps, and the system evolves through multiple thermodynamics (ambient and extreme conditions) and electronic (metal and insulator) states. We show that ChIMES, a generalized many-body reactive force field machine-learned to density functional theory (DFT) molecular dynamics trajectories, is able to retain the accuracy of DFT simulation in describing structural properties and chemistry for a wide range of thermodynamics states while increasing orders of magnitude in computational efficiency. Shock compression simulations show that the developed ChIMES model can capture the ultrafast chemical reactions of HN₃.